Some baby mice born in Japan are living proof that mouse stem cells taken from embryos or created by reprogramming fetal tissue can be used to make viable egg cells.

Researchers had already created functional sperm from stem cells, and some groups have reported making eggs, or oocytes, but those had never been shown to produce offspring. Now, Mitinori Saitou of Kyoto University in Japan and colleagues have coaxed mouse stem cell to make eggs that produce normal, fertile offspring, the resea...